Lewis, S.D., Behrmann, J.H., Musgrave, R.J., and Cande, S.C. (Eds.), 1995Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 141

30. BIOSTRATIGRAPHIC AND PALEOCEANOGRAPHIC SYNTHESISOF ODP LEG 141, OFF SOUTHERN CHILE1

Dorothee Spiegler,2 Carla Muller,3 Sigurd Locker,2 and Joachim Schönfeld2

ABSTRACT

Bioevents of calcareous and siliceous nannofossils and microfossils were used to establish biostratigraphic zonations forPliocene to Quaternary sections recovered at Sites 859 through 863 off southern Chile during Ocean Drilling Program Leg 141.Stable oxygen isotope data from Site 861 were employed to subdivide the upper Quaternary sequence, which is the first attemptat directly correlating oxygen isotope events from the southeastern Pacific with the SPECMAP stack. Paleomagnetic data couldnot be used for age calibration because paleomagnetic signals are strongly overprinted. Paleoceanographic inteΦretations arebased on microfossil records as well as on stable oxygen isotopes measured from foraminifers at Site 861.

INTRODUCTION

During Ocean Drilling Program (ODP) Leg 141, Quaternary toPliocene sedimentary sequences were encountered in 13 holes drilledat five sites between 45° and 47°S, off the coast of southern Chile(Fig. 1). In this region the active oceanic spreading center of the ChileRidge is subducted under the continental plate of South America. Themain objectives of ODP Leg 141 were to investigate the geologic andtectonic processes associated with the subduction of oceanic crust andsediment material under the continental crust of the South AmericanPlate. The sedimentary sequences recovered consist of predominantlyclayey to silty sediments that vary in consolidation because of tec-tonic processes at the accretionary wedge. The sediments yielded rareto common calcareous and siliceous nanno- and microfossils includ-ing coccolithophorids, planktonic and benthic foraminifers, silico-flagellates, ebridians, actiniscidians, diatoms, andradiolarians, whichwere used for stratigraphic and paleoceanographic interpretations.Additionally, stable oxygen and carbon isotopes were analyzed frombenthic and planktonic foraminifers found in Quaternary sedimentsat Site 861.

BIOSTRATIGRAPHY

Biostratigraphy of Pliocene to Quaternary sediments is stronglyinfluenced by paleoceanography. The zonations used for ODP Leg141 are high latitude subdivisions that can be recognized in bothhemispheres, and which differ distinctly from zonations described formid and low latitudes.

The age determinations primarily conducted on calcareous nan-noplankton and planktonic foraminifers are supported by results fromsilicoflagellate, ebridian, and benthic foraminifer studies. Both dia-toms and radiolarians are present within the upper portions of thedrilled sequences, but downhole they are absent or too rare to beuseful for stratigraphic subdivisions. The zonations of the microfossilgroups used and their correlations are summarized in Figure 2.

Generally, the biostratigraphic resolution is rather low owing tothe scarcity of microfossils and the low diversity of assemblages thatembrace mainly long ranging species of minor stratigraphic value.Low abundancy and diversity may be related to oceanographical and

1 Lewis, S.D., Behrmann, J.H., Musgrave, R.J., and Cande, S.C. (Eds.), 1995. Proc.ODP, Sci. Results, 141: College Station, TX (Ocean Drilling Program).

Research Center for Marine Geosciences, Wischhofstrasse 1-3, Building 4, D-24148Kiel, Federal Republic of Germany.

3 Institute of Geology and Paleontology of the Johann-Wolfgang-Goethe University,Senckenberg-Anlage 32-43, D-60325 Frankfurt/Main, Federal Republic of Germany.

sedimentological factors (i.e., low surface-water paleotemperatures,dissolution of skeletons during and after deposition, and dilution ofparticles by high amounts of advected sediment). Dissolution ofcalcareous and siliceous nanno- and microfossils is probably affectedto some extent by fluid circulation and compression within the accre-tionary wedge. Stress related to shearing within the wedge is evi-denced by deformed foraminifers (Spiegler and Muller, this volume).

The biostratigraphy of calcareous nannoplankton from Sites 859to 863 is summarized in Spiegler and Muller (this volume). Agedeterminations are based on the standard nannoplankton zonation ofMartini (1971), which, however, is difficult to apply in higher lati-tudes due to low diversity assemblages. Nevertheless, the Pleistoceneoff southern Chile can be subdivided with some restrictions intoZonesNN19toNN21.

The first appearance (FA) of Emiliania huxleyi, which indicatesthe base of Zone NN21, usually falls within oxygen isotope Stage 8at 0.27 Ma (Thierstein et al., 1977). However, at Site 861 the firstoccurrence (FO) of Emiliania huxleyi was determined in Section141-861C-4H-CC at 31.5 mbsf within the younger Stage 6. Thisdiscrepancy might be due to the scarcity of Emiliania huxleyi belowisotope Event 5. The nannoplankton Zone NN20/19 boundary, de-fined by the last appearance (LA) of Pseudoemiliania lacunosa, maybe recognized in higher latitudes. It marks the lower/upper Pleisto-cene boundary at 0.47 Ma.

In this study, the Pliocene/Pleistocene boundary is determined bythe FA of Gephyrocapsa oceanica at 1.6 Ma (Raffi and Rio, 1979),which corresponds to an elevated top of Zone NN18 compared withBerggren et al. (1985). The FA of G. oceanica coincides roughly withthe last occurrence (LO) of Cyclococcolithus macintyrei and theextinction of discoasters, which conventionally define the Pliocene/Pleistocene boundary. However, Cyclococcolithus macintyrei is toorare within the study area to be useful for biostratigraphic distinctions,and discoasters are missing in these latitudes.

The upper Pliocene cannot be subdivided using calcareous nan-noplankton, since index fossils are missing. The oldest sedimentsrecovered are late Pliocene in age, based on the presence of Pseudo-emiliania lacunosa and small specimens of Gephyrocapsa sp. Suchsediments are not older than 3.2 to 3.4 Ma. Unfortunately, age inter-pretations cannot be calibrated to the geomagnetic polarity pattern,because strong overprinting by high temperature fluids precludescollection of relevant data (Musgrave et al., this volume).

Biostratigraphic results using planktonic foraminifers from Sites859 to 863 are combined with the calcareous nannoplankton stratig-raphy by Spiegler and Muller (this volume). The assemblages ofplanktonic foraminifers observed in the study area are intermediate tothose described from low latitudes (Blow, 1969; Bolli and Saunders,

373

D. SPIEGLER, C. MULLER, S. LOCKER, J. SCHONFELD

78°W IT

45°S

Figure 1. Location map of Leg 141 sites. Bathymetry in meters.

1985; Kennett and Srinivasan, 1983) and those from mid to highlatitudes (Srinivasan and Kennett, 1981). According to present-dayplanktonic foraminifers, the investigated area falls into the southernTransition Zone, which is influenced by the Subtropical Zone and theSubantarctic Zone (Be and Tolderlund, 1971).

The sediments recovered can be attributed to the Truncorotaliatruncatulinoides Zone, the Globoconella inflata Zone, and the Glo-borotalia crassaformis Zone. Since the FO of T. truncatulinoides isstrongly influenced by paleotemperatures, the base of this zone ap-

pears diachronous (Jenkins and Gamson, 1993). The FA of G. inflataconventionally marks the early/late Pliocene boundary. Generally,abundance and diversity of the planktonic foraminifer assemblagesfound in Pliocene to lower Pleistocene sediments are low.

Beneath the cover of upper Pliocene to Pleistocene sediments atSite 862 off Taitao Ridge a sequence of rhyolitic and phyric basaltsoccurs. Intercalated in the basaltic sequence, a marine sandstone wasfound. The fine-grained portion of this sandstone yielded a number oflate Paleocene planktonic and benthic foraminifers (Forsythe et al.,

374

BIOSTRATIGRAPHIC AND PALEOCEANOGRAPHIC SYNTHESIS

0.27

0.47

0.65

1.60

3.20 —

Calcareousnanno-planktonzone

NN21

NN20

NN19

NN18

NN16

NN15

Planktonic foraminifer zone

Low Mid HighLatitudes

G. marg. G. crassaformi

Silicoflagellatezone

D. m. acul.

Distephanusspeculum

Distephanusaculeatus

Unzoned

Ebridian/Actiniscidianzone

Actiniscuspentasterias

Ammodochiumserotinum

Unzoned

Benthicforaminiferzone

Uvigerinasenticosa

Orthomor-phina cf.consobrina

Uvigerinamantaensis

Figure 2. Biozonations applied for Leg 141. D. m. αcul. = Dictyochα messαnensis αculeαtα, G. = Globorotαliα.

this volume). The late Paleocene age of the sediment contrasts withthe Pliocene age of overlying volcanics and sediments.

The biostratigraphy of benthic foraminifers from Site 861 is docu-mented by Schönfeld and Spiegler (this volume). Benthic foramin-ifers off the coast of Chile were first described by Orbigny (1839) andBrady (1884), and more recently by Boltovskoy and Theyer (1970)and Boltovskoy (1976), while Resig (1990) studied benthic foramin-ifers from the low latitudes off the coast of Peru. Although benthicforaminifers are predominantly ecological indicators, a zonationcomprising three assemblage zones could be established for the re-gion off the Chile coast (Fig. 2).

Oxygen and carbon stable isotopes from planktonic and benthicforaminifers are discussed by Schönfeld et al. (this volume). Theoxygen isotope curve obtained from Quaternary sediments at Site 861is correlated with the SPECMAP stack. The data indicate that thesequence down to 73 mbsf extends to oxygen isotope Event 10.2,which is dated at 0.34 Ma.

The biostratigraphies of silicoflagellates and ebridians/actiniscidi-ans are described in Locker (this volume). The assemblages recoveredat Sites 860 and 861 are characteristic of the high latitudes of bothhemispheres. Although species abundances and diversities are low,two biozonations could be distinguished comprising three and twozones, respectively. The LA events of the silicoflagellate Distephanusaculeatus and of the ebridian Ammodochium serotinum are good indi-cators for the Pliocene/Pleistocene boundary in high latitudes. At thesites studied both events approximate the elevated top of Zone NN18at 1.6 Ma, as adopted in Spiegler and Muller (this volume).

No detailed diatom and radiolarian biostratigraphies were elabo-rated for this volume, but initial data may be found in Behrmann et al.(1992). According to Boden (this volume), diatoms cannot be used toprovide biostratigraphic resolution, as they are too rare or the assem-blages are dominated by long ranging species. Ecological preferencesof diatom species indicate that upwelling did not exist off southernChile during Neogene time.

Bioevents and related ages are listed in Tables 1 to 3. The mostcomplete biostratigraphic results were obtained from Site 861. Theresults from Sites 859, 860, 862, and 863 are less complete. Figure 3summarizes the biostratigraphic events and age assignments recog-nized for the investigated area.

PALEOCEANOGRAPHY

Documenting Pliocene to Pleistocene climate changes off south-ern Chile will increase our understanding of the climate history ofSouth America. The present climate of southern Chile is stronglyinfluenced by surface-water masses of the southern Pacific, espe-cially those belonging to the subpolar and transitional water belts. Themain influence, however, comes from the subpolar water massesof the Antarctic Circumpolar Current, which approaches the SouthAmerican continent and divides at 39°^0°S. One branch of the cur-rent flows to the south where it joins the Cape Horn Current, the otherturns to the north where it forms the Peru Current. The Peru Currenttransports cold nutrient-rich water northward to 15°S. The current isbounded on the northwest by the Subtropical Convergence, separat-

375

D. SPIEGLER, C. MULLER, S. LOCKER, J. SCHONFELD

Table 1. Biostratigraphic events obtained from Site 859.

Core, section, Depth Ageinterval (cm) (mbsf) (Ma) Event Series

141-859 A-2H-CC4H-CC

I4I-859B-29R-CC37R-CC

10.74 <0.27 F0 Emiliania huxleyi (N), Tntncorotalia truncatulinoides (PF) Pleistocene25.00 >0.47 LO Pseudoemiliana lacunosa (N)

389.20 <3.2O FO Globoconella inflata (PF) upper Pliocene466.40 <3.20 FO Pseudomiliania lacunosa (N), Gephyrocapsa sp., small (N)

Note: FO = first occurrence, LO = last occurrence, N = calcareous nannoplankton, PF = planktonic foraminifer.

Table 2. Biostratigraphic events obtained from Site 860.

Core, section. Depthinterval (cm) (mbsf)

Age(Ma) Event Series

14I-860B-2H-2.60 3.50 <0.27 F0 Emiliania huxleyi (N) upper Pleistocene

I0H-CC 78. I0 LO Helicospaera selilii (N)16X-3. 32 120.12 < 1.60 FO Gephyrocapsa oceanica (N), Tnmcorotalia truncatulinoides (PF) lower Pleistocene

17R-3. 128 130.78 >l .60 F0 Cyclococcolithus macintyrei (N) upper Pleistocene19X-3, 100 141.10 >1.60 LO Ammodochium sp. (E)21R-1, 72 156.22 >1.60 LO Distephanus aculeatus (S)22X-2, 103 167.63 >l .70 LO Ammodochium serotinum (E)62X-3, 114 535.04 <3.20 F0 Globoconella inflata (PF)

Note: F0 = first occurrence, LO = last occurrence, N = calcareous nannoplankton, PF = planktonic foraminifer, S = silicoflagellate, Eebridian.

Table 3. Stratigraphic events obtained from Site 861.

Core, section,interval (cm)

Depth(mbsf)

Age(Ma) Event Series

861B-1H-1.75861C-IH-2. 87861B-IH-4.4186IB-1H-5, 115861C-2H-5. 80861A-IH-4. 109861C-2H-CC86IC-3H-2, 7086IC-3H-5. 60861C-4H-4, 109861C-4H-CC86IC-5H-4, 7086IC-5H-CC861C-6H-3, 56861C-7H-3, 3986IC-8H-CC86IC-10H-2, 73

861C-15H-CC86IC-I6X-4. 3086IC-I9X-I.6086IC-20X-CC

861C-21X-1. 10086IC-22X-4, 8786ID-8R-1.46

0.752.374.917.159.80

11.1912.5014.7019.1027.5931.5035.5041.0044.5652.8069.5073.23

128.90133.70158.90170.20

171.20185.30410.26

0.00980.01240.01830.0235

<0.0270.0530.0650.0800.1220.135

<0.2700.1710.1940.2490.3100.3310.341

0.47<1.60

1.301.60

>1.60>1.60<3.2O

Oxygen isotope Event 1.1 upper PleistoceneBeginning of Termination IbBeginning of Termination laOxygen isotope Event 2.2FCO Dictyocha messanensis aculeata (S)Oxygen isotope Event 3.3Oxygen isotope Event 4.2Oxygen isotope Event 5.1Oxygen isotope Event 5.5Oxygen isotope Event 6.2F0 Emiliania huxleyi (N)Oxygen isotope Event 6.5Oxygen isotope Event 7.1Oxygen isotope Event 8.2Oxygen isotope Event 9.1Oxygen isotope Event 9.3Oxygen isotope Event 10.2

LO Pseudoemiliania lacunosa (N) lower PleistoceneF0 Truncorotalia tnmcatulioides (PF)LO Orthomorphia cf. consobrina (BF)FO Gephyrocapsa oceanica (N)

LO Distephanus aculeatus (S) LO Ammodochium sp. (E) upper PlioceneLO Ammodochium serotinum (E)F0 Globoconella inflata (PF)

Note: FCO = first consistent occurrence, FO = first occurrence, LO = last occurrence, N = calcareous nannoplankton, PF = plank-tonic foraminifer, BF = benthic foraminifer, S = silicoflagellate, E = ebridian.

ing the subpolar waters of the Antarctic Circumpolar Current from thetemperate waters of the South Pacific Gyre. The position of the Sub-tropical Convergence shows strong seasonal north-south fluctuations.

An increased abundance of calcareous nannofossils within theearly Zone NN16 might indicate warm surface-water conditions pre-ceding the late Pliocene cooling. However, calcareous and siliceousnanno- and microfossils demonstrate that cooler conditions prevailedduring most of the late Pliocene. The assemblages are generallycharacterized by low species abundance and minor diversity, and bythe presence of the cold-adapted silicoflagellate Distephanus specu-lum. Repeated occurrences of the warm-adapted silicoflagellate Dic-tyocha messanensis messanensis hint at oscillations of the transi-tional water belt during late Pliocene and early Pleistocene times. The

occurrences may reflect mixing of transitional and subpolar watermasses or the replacement of subpolar waters (Locker, this volume).

Variations of stable oxygen isotope values indicate paleotempera-ture fluctuations during the late Pleistocene. The warm intervals of theisotopic record are generally characterized by higher abundance ofplanktonic foraminifers. Although recent warm-water planktonic for-aminifers are not found in the surface waters off the southern Chilecoast, several subtropical species were recovered in uppermost Pleis-tocene sediments, including Globorotaloides hexagonus, Neoglobo-quadrina dutertrei, Beella digitata, Globigerina apertura, and Orbu-lina universa (Spiegler and Muller, this volume). The warm-waterfluctuations of latest Pleistocene time are confirmed by enhanced occur-rences of the warm-adapted silicoflagellate D. messanensis aculeata

376

BIOSTRATIGRAPHIC AND PALEOCEANOGRAPHIC SYNTHESISAg

e (M

a)

0.27

0.47

0.65 _

1 60

3 20

3.40

Serie

sPl

eist

ocen

ePl

ioce

ne

Uppe

Φ

_ l

Upp

erLo

wei

Cal

care

ous

nann

opla

nkto

nzo

ne

NN21

NN20

NN19

NN18

NN16

NN15

_ l FCO

FO

LO

- I LO

J F0LO

-| LO

" I LO

_ l FO

Event

Da. messanensis aculeate

E. huxleyi

P. lacunosa

H. sellii

G. oceanica, T. truncatulinoidesC. macintyrei,A. serotinum, Ds. aculeatus, andO. cf. conεobrina

U. mantaenis

Gl. inflata, P. lacunosa, G. sp. (small)

Figure 3. Biostratigraphic events and their age assignment for Leg 141. F0 =first occurrence, LO = last occurrence, FCO = first consistent occurrence, A. =Ammodochium, C. = Cyclococcolithus, Dα. - Dictyochα, Ds. = Distephαnus,E. = Emiliαniα, G. = Gephyrocαpsα, Gl. = Globoconellα, H. = Helicosphαerα,O. = Orthomorphinα, P. = Pseudoemiliαniα, T. = Truncorotαliα, U. = Uvigerinα.

(Locker, this volume). It is suggested that both subtropical planktonicforaminifers and transitional silicoflagellates were carried by warm-water masses from the Central Pacific to the south by strong El Ninoevents (Locker, this volume; Schönfeld et al., this volume). The warm-water masses transported during these events had a strong impact onthe local climate in southern Chile (Schönfeld et al., this volume).

CONCLUSIONS

1. The combination of bioevents from various plankton groups(calcareous nannoplankton, planktonic foraminifers, silicoflagel-lates, and ebridians) provided a reasonable stratigraphic resolution ofupper Pliocene and Quaternary sediments recovered at Sites 859through 863. The biozonations established represent high latitudesubdivisions, because the study area was mainly influenced by sub-polar water masses.

2. The Pliocene/Pleistocene boundary was determined by the FAof Gephyrocαpsα oceαnicα, which corresponds to an age of 1.6 Ma.The LA events of the silicoflagellate Distephαnus αculeαtus and ofthe ebridian Ammodochium serotinum approach this boundary, thusindicating their stratigraphic value for higher latitudes.

3. Ecological preferences of the plankton species studied enableto describe paleoceanographic developments. The paleoceanographyoff southern Chile was generally characterized by the cold Perucurrent. But according to the occurrences of transitional silicoflagel-

lates and subtropical planktonic foraminifers warmer surface watermasses repeatedly expanded over the study area. The warm-adaptedplankton was carried from the Central South Pacific to the southeastby strong El Nino events.

4. Stable oxygen isotope data indicate distinct paleotemperaturefluctuations during the late Pleistocene. The record at Site 861 ex-tends back to oxygen isotope event 10.2, which is 0.34 Ma.

5. It is assumed that future plankton and stable isotope studieswill lead to important insights into the variation of Quaternary paleo-climate and the interaction between ocean and continent of mid tohigh southern latitudes.

REFERENCES*

Be, A.W.H., and Tolderlund, D.S., 1971. Distribution and ecology of livingplanktonic foraminifera in surface waters of the Atlantic and IndianOceans. In Funnel, B.M., and Riedel, W.R. (Eds.), The Micropaleontologyof Oceans: Cambridge (Cambridge Univ. Press), 105-149.

Behrmann, J.H., Lewis, S.D., Musgrave, R.J., et al., 1992. Proc. ODP, Init.Repts., 141: College Station, TX (Ocean Drilling Program).

Berggren, W.A., Kent, D.V., Flynn, J.J., and Van Couvering, J., 1985. Neogenegeochronology and chronostratigraphy. In Snelling, NJ. (Ed.), The Chro-nology of the Geological Record. Geol. Soc. London Mem.,10:211-250.

Blow, W.H., 1969. Late middle Eocene to Recent planktonic foraminiferal bio-stratigraphy. In Brönniman, P., and Renz, H.H. (Eds.), Proc. First Int. Conf.Planktonic Microfossils, Geneva, 1967: Leiden (E.J. Brill), 1:199-422.

Bolli, H.M., and Saunders, J.B., 1985. Oligocene to Holocene low latitudeplanktonic foraminifera. In Bolli, H.M., Saunders, J.B., and Perch-Nielsen,K. (Eds.), Plankton Stratigraphy: Cambridge (Cambridge Univ. Press),155-262.

Boltovskoy, E., 1976. Distribution of Recent foraminifera of the South Ameri-can region. In Hedley, R.H., and Adams, CG. (Eds.), Foraminifera (Vol.2): London (Academic Press), 171-237.

Boltovskoy, E., andTheyer, R, 1970. Foraminiferos recientes de Chile Central.Rev. Mus. Argent. Cienc. Nat. "BernadinoRivadavia," HidrobioL, 2:279-379.

Brady, H.B., 1884. Report on the Foraminifera dredged by H.M.S. Challenger,during the years 1873-1876. Rep. Sci. Results Challenger Exped., Zool,9:1-814.

d'Orbigny, A., 1839. Voyage dans 1'Amerique Meridionale—foraminiferes.Ann. Sci. Nat., Sen 5, 5:1-86.

Jenkins, D.G., and Gamson, P., 1993. The late Cenozoic Globorotalia trunca-tulinoides datum-plane in the Atlantic, Pacific and Indian oceans. InHailwood, E.A., and Kidd, R.B. (Eds.), High Resolution Stratigraphy.Geol. Soc. Spec. Publ. London, 70:127-130.

Kennett, J.P., and Srinivasan, M.S., 1983. Neogene Planktonic Foraminifera:A Phylogenetic Atlas: Stroudsburg, PA (Hutchinson Ross).

Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplanktonzonation. In Farinacci, A. (Ed.), Proc. 2nd Int. Conf. Planktonic Microfos-sils Roma: Rome (Ed. Tecnosci.), 2:739-785.

Raffi, I., and Rio, D., 1979. Calcareous nannofossil biostratigraphy of DSDPSi te 132—Leg 13 (Tyrrhenian Sea-Western Mediterranean). Riv. Ital.Paleontol. Stratigr., 85:127-172.

Resig, J.M., 1990. Benthic foraminiferal stratigraphy and paleoenvironmentsoff Peru, Leg 112. In Suess, E., von Huene, R., et al., Proc. ODP, Sci.Results, 112: College Station, TX (Ocean Drilling Program), 263-296.

Srinivasan, M.S., and Kennett, J.P., 1981. A review of Neogene planktonicforaminiferal biostratigraphy: applications in the equatorial and SouthPacific. In Warme, J.E., Douglas, R.G., and Winterer, E.L. (Eds.), TheDeep Sea Drilling Project: A Decade of Progress. Spec. Publ.—Soc. Econ.Paleontol. Mineral., 32:395-432.

Thierstein, H.R., Geitzenauer, K., Molfino, B., and Shackleton, NJ., 1977.Global synchroneity of late Quaternary coccolith datum levels: validationby oxygen isotopes. Geology, 5:400^1-04.

* Abbreviations for names of organizations and publications in ODP reference lists followthe style given in Chemical Abstracts Service Source Index (published by AmericanChemical Society).

Date of initial receipt: 9 May 1994Date of acceptance: 8 November 1994Ms 141SR-036

377